1. Field of the Invention
The present invention relates to a hard disk drive which is used as an auxiliary memory device of a computer, and more particularly, to a control method for controlling the floating displacement of a flying magnetic head with respect to a disk, and a device therefor.
2. Description of Related Art
A hard disk drive in which information is recorded or reproduced is usually used as an auxiliary memory device of a personal computer. Recently, the storage capacity of the hard disk drive has increased significantly, whereas the size thereof has gradually been reduced. Accordingly, the track pitch of a disk and the bit cell thereof become finer and finer. Thus, a servo control technology for floating a magnetic head at a constant and fine interval throughout the disk region is required to record or reproduce information on such a disk.
FIG. 1 shows a conventional hard disk drive Referring to FIG. 1, at least one magnetic disk 11 is rotatably mounted on a spindle motor (not shown) installed on a base frame 10. Also, a magnetic head actuator 20 for pivoting around a pivot shaft to fly a magnetic head (h) on the disk 11 is included.
The magnetic head actuator 20, as shown in FIG. 2, includes a swing arm 23 which is pivoted around a shaft 22 by a voice coil motor 21, a suspension 24 installed on the swing arm 23, and a magnetic head (h) fixed on a gimbal 25 installed at the end of the suspension 24. Reference numeral 30 is a circuit driving portion which controls the transmission of a signal between a main circuit board, interfaced with a main body such as a computer, and the magnetic head (h), and also controls the driving of the actuator 20.
In the operation of the hard disk drive, the magnetic head (h) detects information from tracks on the disk 11 while moving in a radial direction of the disk 11 according to the driving of the actuator 20. The magnetic head (h) is in contact with the disk 11 at the beginning of the operation of the disk driver, and then rises to a certain height from the disk 11 as the rotating speed of the disk 11 gradually increases. That is, since the magnetic head (h) contacts the disk 11 at the initial operation of the disk driver, abrasion of the magnetic head occurs. Also, the magnetic head may be damaged by an impact generated when the magnetic head (h) lands on the surface of the disk 11 after the operation of the disk driver.
In order to solve the above problem, the conventional hard disk drive includes a vibration detecting sensor 40 for detecting and controlling the flying displacement of the magnetic head (h), as shown in FIG. 1.
The vibration detecting sensor 40 includes two thin piezo-electric elements 41 and 42 which are joined to each other and capable of having opposite polarities, as shown in FIG. 3. The vibration detecting sensor 40 is installed on the base frame 10 such that one end is fixed and the other end is free. For example, when an impact or vibration is transmitted from an external source, the free end is displaced to thus warp the piezo-electric elements 41 and 42 as shown in FIG. 3, thereby generating an electric charge. A voltage signal generated according to the above is transmitted to the magnetic head actuator 20, so that information recording or reproduction by the magnetic head (h) is temporarily halted. Therefore, after the cause of the vibration is removed, the recording or reproduction can be resumed from the halted state.
However, the degree of displacement of the flying magnetic head detected by the vibration detecting sensor 40 varies depending on the position where the sensor is installed and the source of the external vibration. Furthermore, since the base frame 10 is made of a rigid material which can absorb vibration, the sensor 40 cannot detect minor impacts or vibrations. In particular, in the case of a high density disk whose track pitch is very fine, the reliability of the detection is further deteriorated, and it is difficult to achieve an active control algorithm which can correct the generation of the displacement in real time.
FIGS. 4 and 5 show a conventional magnetic head actuator for actively controlling the flying displacement of a magnetic head due to an external impact or vibration. Like reference numerals as those in the above-mentioned drawings denote the same components. Referring to FIGS. 4 and 5, a piezo-electric polymer element 26 which acts as a sensor for detecting a displacement due to an impact or vibration, is attached to one surface of the suspension 24. A piezo-electric ceramic element 27, which is a correction actuator for receiving a signal indicating the amount of displacement detected by the piezo-electric polymer element 26 and correcting the suspension 24 to a normal position, is attached to the opposite surface of the suspension 24. In FIG. 5, reference numeral 50 is a control circuit driving portion for connecting the piezo-electric polymer 26 to the ceramic element 27.
The piezo-electric polymer element 26 detects the displacement of the suspension 24 involved with displacement of the magnetic head h, to detect the displacement of the magnetic head h. Information on the detected amount of displacement is transmitted to the control circuit driving portion 50, signal-processed, and input to the piezo-electric ceramic element 27. Then, the piezo-electric ceramic element 27 generates a correction force corresponding to the amount of displacement, to restore the suspension 24 to a normal position. Thus, the magnetic head h can be maintained at a constant flying height.
However, since the piezo-electric polymer element 26 is attached to the upper or lower surface of the suspension 24, it can detect only an upward or downward vibration displacement of the magnetic head h. Accordingly, since a displacement due to an impact or vibration in a lateral direction cannot be detected, in the case of a high density disk whose track pitch is very fine, the magnetic head h is displaced to an adjacent track even by a minute impact or vibration, which causes a malfunction. Also, the piezo-electric polymer element 26 is greatly influenced by the surrounding temperature, so that the reliability of displacement correction is degraded. Furthermore, a lead wire which is connected to the piezo-electric polymer element to provide starting power may be disconnected depending on the rotation of the suspension 24.